β-lapachone (3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione), a quinone, is derived from lapachol (a naphthoquinone) which can be isolated from the lapacho tree (Tabebuia avellanedae), a member of the catalpa family (Bignoniaceae). Lapachol and β-lapachone (with numbering) have the following chemical structures:

β-lapachone, as well as its intermediates, derivatives and analogs thereof, are described in Li, C. J. et al., (1993) J. Biol. Chem., 268(30): 22463-22468. As a single agent, β-lapachone has demonstrated significant antineoplastic activity against human cancer cell lines at concentrations typically in the range of 1-10 μM (IC50). Cytotoxicity has been demonstrated in transformed cell lines derived from patients with promyelocytic leukemia (Planchon et al., (1996) Cancer Res., 55: 3706-3711), prostate (Li, C. J., et al., (1995) Cancer Res., 55: 3712-3715), malignant glioma (Weller, M. et al., (1997) Int. J. Cancer, 73: 707-714), hepatoma (Lai, C. C., et al., (1998) Histol Histopathol, 13: 89-97), colon (Huang, L., et al., (1999) Mol Med, 5: 711-720), breast (Wuertzberger, S. M., et al., (1998) Cancer Res., 58: 1876), ovarian (Li, C. J. et al., (1999) Proc. Natl. Acad. Sci. USA, 96(23): 13369-13374), pancreatic (Li, Y., et al., (2000) Mol Med, 6: 1008-1015; Li, Y., (1999) Mol Med, 5: 232-239), and multiple myeloma cell lines, including drug-resistant lines (Li, Y., (2000) Mol Med, 6: 1008-1015). No cytotoxic effects were observed on normal fresh or proliferating human PBMC (Li, Y., (2000) Mol Med, 6: 1008-1015).
β-lapachone appears to work by inducing unscheduled expression of checkpoint molecules, e.g. E2F, independent of DNA damage and cell cycle stages. Several studies have shown that β-lapachone activates the E2F1 checkpoint pathway and induces cell death in cancer cells from a variety of tissues without affecting normal cells from these tissues (U.S. Patent Application Publication No. 2002/0169135, incorporated by reference herein). In normal cells with their intact regulatory mechanisms, such an imposed expression of a checkpoint molecule results in a transient expression pattern and causes little consequence. In contrast, cancer and pre-cancer cells have defective mechanisms, which result in unchecked and persistent expression of unscheduled checkpoint molecules, e.g. E2F1, leading to selective cell death in cancer and pre-cancer cells.
In addition to β-lapachone, a number of β-lapachone analogs having antiproliferative properties have been disclosed in the art, such as those described in PCT International Application PCT/US93/07878 (WO94/04145), which is incorporated by reference herein, and U.S. Pat. No. 6,245,807, incorporated by reference herein, in which a variety of substituents may be attached at positions 3- and 4- on the β-lapachone compound. PCT International Application PCT/US00/10169 (WO 00/61142), incorporated by reference herein, discloses β-lapachone, which may have a variety of substituents at the 3-position as well as in place of the methyl groups attached at the 2-position. U.S. Pat. Nos. 5,763,625, 5,824,700, and 5,969,163, each of which is incorporated by reference herein, disclose analogs and derivatives with a variety of substituents at the 2-, 3- and 4-positions. Furthermore, a number of journals report β-lapachone analogs and derivatives with substituents at one or more of the following positions: 2-, 3-, 8- and/or 9-positions, (See, Sabba et al., (1984) J Med Chem27:990-994 (substituents at the 2-, 8- and 9-positions); (Portela and Stoppani, (1996) Biochem Pharm 51:275-283 (substituents at the 2- and 9-positions); Goncalves et al., (1998) Molecular and Biochemical Parasitology 1:167-176 (substituents at the 2- and 3-positions)).
Moreover, U.S. Patent Application Publication No. 2004/0266857 and PCT International Application PCT/US2003/037219 (WO 04/045557), incorporated in by reference herein, disclose and several journal reports describe structures having sulfur-containing hetero-rings in the “α” and “β” positions of lapachone (Kurokawa S, (1970) Bulletin of The Chemical Society of Japan 43:1454-1459; Tapia, R A et al., (2000) Heterocycles 53(3):585-598; Tapia, R A et al., (1997) Tetrahedron Letters 38(1):153-154; Chuang, C P et al., (1996) Heterocycles 40(10):2215-2221; Suginome H et al., (1993) Journal of the Chemical Society, Chemical Communications 9:807-809; Tonholo J et al., (1988) Journal of the Brazilian Chemical Society 9(2):163-169; and Krapcho A P et al., (1990) Journal of Medicinal Chemistry 33(9):2651-2655). These findings encourage the design and synthesis of new lapachone derivatives and analogs and their evaluation for antiproliferative activity in a variety of biological systems.